1. Field of the Invention
This invention relates generally to radio communication apparatus including a mobile radio communication system. More specifically, it relates to a method of controlling the transmission and reception of frames of a Code Division Multiple Access (CDMA) communication system.
2. Description of the Background Art
In a conventional mobile radio communication system, a transmission channel and a reception channel are provided for communication between a base station and one or more mobile stations.
The operation of a conventional CDMA system is as follows. Assume that a mobile station is transmitting a user information signal (e.g. a signal transmitting voice and/or data) over the transmission channel to a base station. In the transmitter of the mobile station, the user information signal is assigned to a predetermined frame, error corrected, modulated, the output of the modulator spread with a user information spreading code such as a pseudo-random number code, and the spread user information signal combined with a header. The header is then spread by use of a spreading code and the spread header used to synchronize the transmitting station with the base station receiver. The spread user information signal and the spread header are up-converted to a transmission signal having a radio frequency bandwidth and then radiated via an antenna to the receiver of the base station.
The transmission signal coupled to the base station receiver is down-converted to the spread user information signal and the spread header. The down-converted spread user information signal is next despread by means of the user information spreading code, the spread header despread by means of the header spreading code, and the header used to detect the head of the frame. After the head of the frame has been detected, the user information signal is demodulated and decoded. The user information signal is then transmitted to a remote communication apparatus such as another mobile station in the system or a telephone in the public telephone network.
In the conventional CDMA mobile radio communication system, the base station transmits back to the mobile station which originated the user information signal either an acknowledged signal (ACK) or a not acknowledged signal (NAK). The base station sends either an ACK or an NAK signal to the mobile station after receiving the user information signal to indicate to the mobile station whether or not a signal has been received from the mobile station. This acknowledgment is needed because not all transmission paths between the mobile and base stations are reliable and not all transmitted user information signals reach the base station. If the mobile station receives an NAK signal, it retransmits the user information signal to the base station.
For example, to confirm that every user information signal transmitted from the mobile station has been correctly received at the base station, a conventional request repeat system of the type described in U.S. Pat. No. 4,779,274 is provided. In the request repeat system, if the base station does not receive a user information signal or finds errors in the user information signal of a frame, it requests the mobile station to repeat the user information signal. The mobile station then retransmits the user information signal after inserting an individual transmission number into the data portion of each frame. After receiving this signal, the base station inserts into the data portion of the frame either an ACK or NAK signal corresponding to the transmission number and sends the ACK or NAK signal and the transmission number via the reception channel to the mobile station.
In another method of transmitting the ACK signal or NAK signal, the receiving station may transmit the ACK signal or NAK signal by using a third channel assigned for the exclusive use of the ACK and NAK signals. However, if a third channel is used for transmission of the ACK and NAK signals, the transmission efficiency of the communication between the two stations is reduced because additional equipment is needed, the ACK and NAK signals occupy a part of the user information signal in each frame and each acknowledge signal provides only a small amount of information.
Therefore, it is an object of the present invention to provide a mobile radio communication system and a radio communication apparatus that maintains high transmission efficiency and positively receives the transmitted frame.
To accomplish these objectives, a radio communication system is provided for communicating between a base station and a mobile station by means of frames, each frame including a header and data. The mobile station includes a transmission number provider and a transmission number extractor, the transmission number provider providing a first transmission number to a first frame to be transmitted to the base station, and the transmission number extractor extracting the first transmission number indicated in a header pattern of a second frame transmitted by the base station.
The base station includes a reception number detector and a header provider, the reception number detector detecting the first transmission number included in the first frame transmitted by the mobile station, and the header provider providing the header pattern corresponding to the first transmission number to the second frame. The mobile station retransmits the first frame when the mobile station does not receive the first transmission number indicated in the header pattern of the second frame.
Further, to accomplish these objectives, the radio communication system performs the follow steps:
provides a first transmission number to a first frame at the mobile station;
transmits the first frame from the mobile station to the base station;
extracts the first transmission number from the first frame at the base station;
provides a header pattern corresponding to the first transmission number to a second frame to be transmitted to the mobile station;
transmits the second frame including the header pattern indicating the first transmission number to the mobile station;
extracts the header pattern indicating the first transmission number from the second frame at the mobile station; and
re-transmits the first frame to the base station when the mobile station can not receive the header pattern indicating the first transmission number.